British Destroyer Director Firing System

Director Firing System (sans Henderson Gear) c. 1918

The British Destroyer Director Firing System was deployed late in the war to provide their destroyers and flotilla leaders with the benefits of director firing. It used a crew of three at the director and a fixed elevation angle for firing on the roll. One of the most notable characteristics of the system was that it included cross-levelling to factor out trunnion tilt – a feature mandated by the lively rolling of destroyers and one missing in the Royal Navy's capital ship director system.

Nature

The smaller ships of the Royal Navy were not suitable for the bulky equipment that comprised the director firing systems used in capital ships, but some simplifications and compromises were seen as helpful in preserving the basic benefits in a compact embodiment.

The director could also signal the training angle for the ship's searchlights.

The basic design proved sound enough that the Handbook was receiving minor addenda as late as 1947 – and these pertained to the methods used in conducting a tilt test.

Director

The director was pedestal-mounted, which meant that the operators stood up and shuffled about the pedestal as it trained upon the target. Like the capital ship system, it transmitted slewing and training angle to the gun mounts, and in the same step-sizes: four arc minutes for training, and two degrees per step for slewing. Firing impulses were likewise transmitted to the guns, always firing on the roll.

Unlike the larger system, however, elevation angles were not transmitted at all; the guns were all elevated to a fixed index-mark so they would match the sighting angle of the director's telescope. Henderson Firing Gear was provided if the director layer wished to use it.

The gearing was set up such that the slewing handle rotated the director fifteen times as fast (6° per revolution) as the training handle did (40 arc minutes per revolution).

Tilt correction was addressed in the simplest possible way: by using two wedge-shaped rings at the base of the director to neutralise a tilt of up to 1°. Dip was entirely ignored.

Director Crew

The director eventually required a crew of three after cross-level correction was added.

Cross-Level Operator

Cross-Levelling Gear
The range and cross-tilt inputs are translated into a deflection correction of the director.

This man looked through an open sight arranged 90 degrees off the scopes in azimuth and sought to keep it on the horizon by use of a elevating handwheel. The eyepiece for his open sight could be placed on either end of the assembly to suit any constraints on physical movement about the director. He used a second handwheel to enter the range onto a graduated scale to establish the training correction on the director to provide the proper correction required by the canted trunnions.

At night, the this man also acted as sightsetter for the searchlight deflection dial.

Director Layer

The director layer on this device both trained and elevated the director. He also worked the firing pistol and adjusted the Henderson gyroscope. Since the Henderson gear would keep his horizontal wire on the target, he could concentrate on keeping the scope always on for training. Firing by Henderson was the preferred mode, with firing by the director layer an alternative method. Firing individually at the guns was preferred for close-range night fighting.

Continuous training was to be used as far as practicable, with practice being used to allow anticipation of yaw motions to cause the minimum required number of training reversals.

The second addendum to the handbook, issued in mid-1928, specifies that the training had been sped up by 50% by use of a new training worm wheel and related mechanisms.

Sightsetter

The sightsetter only set the deflection as directed; the gunsights at the guns worked in concert with the mechanical elevation indexes to establish the proper elevation for the range. The director's deflection drum featured a movable pointer which would be adjusted for the range in use, and this would correct for drift. He was required to check the deflection after adjusting the drift pointer, as it would be changed, and he verified the elevation index being used by the director's telescope to ensure common settings at the guns.

Gun Crews

Gunlayer Controls, 4.7-in on C.P. VI Mounting

Training Receiver

Trainer Controls, 4.7-in on C.P. VI Mounting

The gun crews functioned as usual, except as follows. The installation of the director-associated gear varied from mounting to mounting, but these illustrations convey the essence.

The gunlayer, rather than using his handwheel to keep his crosshairs on the target, would use it to keep a newly-fashioned pointer attached to the sight in line with a given index mark on an arc attached to the mounting. The arc had a series of indices arrayed at one degree intervals numbered 6 through 14. The "10" mark was the one ordinarily used, and corresponded to the director's scopes being in the same plane as the guns; the other marks could allow for super-elevation or firing at different points on the roll.

The Sightsetter would be largely idle. He would continue to receive indications of range and deflection, which he might apply to his sight, but these would only be used should resort to local laying be required. Otherwise, he would merely call out changes in gun range.

The Trainer, rather than using his handwheel to keep his crosshairs on the target would instead use it to satisfy a purpose-mounted F.T.P. Training Receiver to keep the gun on the target bearing plus deflection for hitting the target. Convergence for his gun to hit the target would be established by him setting the ranges called out by the sightsetter on a convergence corrector on his receiver.

Searchlight Crew

The man training each searchlight would have a bearing receiver very similar to the training receiver used at the guns, except that the deflection sent to the training receivers would be factored out at the director from its signals. The bearing receiver also corrected for convergence.

Circuitry

Firing Circuits

Training and Slewing Circuits

Adoption

Although it was approved in 1917 to fit this equipment in almost all Flotilla Leaders and all destroyers of "V" class and later, no installations were completed before 1918. However, once things got underway, progress was rapid, as 118 ships were equipped during 1918.

Installations in a total of 149 ships in 1918 ran as follows:

Month (1918)	Flotilla Leaders	Destroyers
		"V" class	"S" class	"L" to "R" classes
February	2	6	–	–
March	3	9	2	–
April	5	10	2	–
May	1	2	2	3
June	1	4	2	7
July	1	8	7	6
August	–	4	4	3
September	3	4	12	6
October	3	3	10	14
Total	19	50	41	39
	149 Ships

See Also

• British Adoption of the Director
• British Director Firing Systems

Bibliography

• Admiralty, Gunnery Branch (1917). The Director Firing Handbook. O.U. 6125 (late C.B. 1259). Copy No. 322 at The National Archives. ADM 186/227.
• Admiralty, Gunnery Branch (1918). Director Firing For Flotilla Leaders and Destroyers. Pub. No. B.R. 934 (late O.U. 6127 and C.B. 1461 and 1461(A). The National Archives. ADM 186/234.
• Admiralty, Technical History Section (1919). The Technical History and Index: Fire Control in H.M. Ships. Vol. 3, Part 23. C.B. 1515 (23) now O.U. 6171/14. At The National Archives. ADM 275/19.